I have customer trying to resolve an issue regarding the TPS51604 Synchronous Buck FET Driver. The part is currently in use on our 10-Channel Charger and we have run into a problem where the bootstrap capacitor discharges and is unable to charge when put into DCM mode and the DRVL and DRVH pins are inactive for a period of time. The PWM and SKIP signals are provided by a microcontroller and upon startup are put into a low state.
We thought that making the SKIP pin high and the PWM pin low for a short duration would briefly turn on the low side mosfet and allow the bootstrap capacitor to charge to VDD but that’s not what happens because the low side mosfet never turns on. The part isn’t behaving according to the truth table and I’m wondering if it has anything to do with the fact that the load is a battery and the SW pin is held at a potential equal to the battery voltage.
I researched a similar ticket on the forum (e2e.ti.com/.../1992849) , however our application is a bit different because the load connected to the output is a battery, so placing a pull-down resistor on the SW pin will not pull the voltage down low enough for the bootstrap capacitor to charge (the SW pin sits at approximately 13 volts when PWM is not present). I have a solution that will allow the bootstrap capacitor to charge even in the presence of a battery but it would require a complete hardware redesign and the addition of many more components. If there was some way we could get the low side mosfet to turn on briefly through some combination of PWM and SKIP signals then I believe it would work.